1. Field of the Invention
The present invention relates to a pipe joint made of resin, and in particular, to a pipe joint applied to laying pipes for a high-purity liquid and ultra pure water treated in a production process in various technical fields such as the production of semiconductors, medical supplies and medicines, food processing and the chemical industry.
2. Description of the Prior Art
Conventionally, such pipe joints made of resin having a structure as shown in FIG. 8 are known. The known pipe joint made of resin comprises a joint body 81, an inner ring 82 and a pushing ring 83. The joint body 81 has a receiving port 84, a tapered receiving surface 85 projecting from a base portion of the receiving port 84, and a tapered receiving surface 86 disposed on a tip portion of the receiving port 84. Additionally, an outer periphery of the receiving port 84 is provided with a male thread portion 87. The inner ring 82 includes a connecting portion 89 having a swelling portion 88 whose section is chevron-shaped, and a protruding portion 90. A tip of the protruding portion 90 is provided with a tapered abutting surface 91. The pushing ring 83 includes a pressing portion 92.
According to this pipe joint made of resin, a diameter of an pipe end 7 made of resin forcedly inserted in the connecting portion 89 is increased, thereby forming a tapered abutting surface 93 on an outer peripheral surface of the pipe 7. The end of the pipe 7 is forcedly inserted into the connecting portion 89, the inner ring 82 connected to the pipe 7 is forcedly inserted in the receiving port 84 of the joint body 81 with the result that a female thread portion 94 of the pushing ring 83 previously fitted in the pipe 7 is threadedly connected to a male thread portion 87 of the receiving port 84, thus being fastened. Then, the pressing portion 92 of the pushing ring 83 pushes the inner ring 82 in a pressing direction, and the abutting surface 91 of the inner ring 82 forcedly abuts against the receiving surface 85 of the joint body 81, thereby forming an axial primary sealing portion Sl, and the abutting surface 93 of the pipe 7 forcedly abuts against the receiving surface 86 of the receiving port 84, thereby forming axial secondary sealing portion S2.
In the conventional pipe joint made of resin referring to FIG. 8, the pushing ring 83 is fastened, thus generating a pressing-directional pressing force. Consequently, a sealing surface pressure in an axial direction is generated on two portions of the primary sealing portion S1 and the secondary sealing portion S2.
In such a pipe joint made of resin, creep and stress relaxation are generated with time on the joint body 81 made of resin and the pushing ring 83, the pipe 7 or the like, whereby the sealing surface pressures of the primary sealing portion S1 and the secondary sealing portion S2 are decreased with the result that there has been a fear that the sealing property will be lost relatively early.
Furthermore, in order to secure a predetermined sealing property, the amount of the threaded connection of the pushing ring 83 is controlled by a fastening torque or the like to high accuracy, and a fastening force generated by the pressing ring 83 has been required to be strictly set at a predetermined magnitude. Therefore, there is a problem wherein operational efficiency is lowered and high technique and skill are required in operation.